1. Field of the Invention
This invention relates to an ashless nonphosphorus lubricating oil additive which imparts improved antiwear, antioxidation, and extreme pressure performance. More particularly, the invention relates to a lubricating oil composition containing an amine salt and/or amide of a derivative of thiobenzoic acid.
2. Description of the Prior Art
It is well known that engine lubricating oils require the presence of additives to protect the engine from wear. Phosphorus-containing additives have been used for this purpose in lubricants for many years. Metal organo phosphorodithioates and, in particular zinc dialkyldithiophosphate (ZDDP), have been used in crank case lubricants for many years as anti-oxidants and anti-wear/load carrying additives. Unfortunately, the presence of phosphorus and/or metals in crank case lubricants has been implicated either in the deactivation of emission control catalysts used in automotive exhaust systems or in deposit and sludge formation. There exists, therefore, a need for an ashless, nonphosphorus containing lubricating oil for use in gasoline and diesel engines.
The use of amine salts of certain benzoic acid derivatives as extreme pressure EP agents for water-based metal cutting fluids has been described in the literature. For example, Japanese Pat. No. 55023132 describes a water-based metal cutting fluid containing an EP agent comprised of an alkali metal salt, an ammonium salt, an amine salt, or an ester of a halogenated benzoic acid derivative such as hydroxy benzoic acid, alkoxy benzoic acid, alkyl benzoic acid etc. The EP agent is claimed to have excellent lubricating property, rusting resistance, and EP properties as compared with conventional nitrites typically used for water-based metal cutting fluids.
The use of substituted benzoic acids as EP agents in water-based fluids is also described in U.S. Pat. No. 4,569,776. For example, this patent discloses a water-based hydraulic fluid composition comprising substituted aromatic compounds like benzoic acids, aromatic sulfonic acids, phenyl alkyl acids and substituted benzenes. Examples of these compounds include mono-, di-, and triaminobenzoic acids; alkylsubstituted (C.sub.1 to C.sub.12 atoms) mono-, di-, and triaminobenzoic acids and mono-, di-, and trialkoxy (C.sub.1 to C.sub.12 atoms) benzoic acids.
U.S. Pat. No. 4,434,066 discloses a water based hydraulic fluid containing a combination of a hydroxyl-substituted aromatic acid component and a nitroaromatic compound component. Suitable acidic materials include saturated and unsaturated aliphatic carboxylic and polycarboxylic acids having at least six carbon atoms, aromatic carboxylic acids and alkali metal or organic amine salts of said aliphatic and aromatic acids.
U.S. Pat. No. 4,012,331 discloses a lubricating oil composition comprising a sulfur compound prepared by reacting a trithiolan compound with a thoil compound in the presence of a base where the thio compound comprises thiophenol, thiosalicylic acid, thioacetic acid, thioglycolic acid, thiobenzoic acid, etc., including an amine or alkali metal salt thereof.